Among the most commonly used types of cylinder locks are those which employ a rotatable plug with a generally longitudinal keyway that receives a flat elongated properly bitted key. Typically the plug is mounted in a cylindrical shell that has at least one longitudinal groove in its internal periphery and the plug carries combinated tumblers, which may be discs or pins that are normally biased to prevent rotation of the plug when the combinating tumblers extend into the shell groove. Insertion of a properly bitted key in the keyway aligns the combinated tumblers with a shear position allowing the plug to rotate in respect to the shell.
Due to the fact that numerous lock manufacturers offer these types of locks which constitute the highest volume ones demanded and lowest cost ones, such as a five disc tumbler lock, each manufacturer attempts to provide a key blank specific to its own produced locks by using special wardings on the key that match its plug keyway employing differently located longitudinal ribs. Since there are so many different key blank configurations, locksmiths, hardware stores and the like who cut keys need to maintain large stocks of the different key blanks in order to cut new or additional keys. For many years now, removable and replaceable plugs have been utilized such as, for example, those of Shinn U.S. Pat. No. 1,805,891 and Falk U.S. Pat. Nos. 1,990,934 and 2,061,456. Although, this approach of plug replacement has provided an alternative to substituting a different key blank when the original is not available, it has not provided a satisfactory solution to the problem of still needing to stock numerous different ones of the key blank configurations.